The present invention relates to an ink jet cartridge which discharges ink using a pressure produced by a bubble and an ink jet recording apparatus which uses the ink jet cartridge.
It has conventionally been known that an ink jet recording apparatus which performs recording by discharging a recording liquid (ink) from an orifice of a liquid ejecting head is a recording apparatus excellent from viewpoints of low noise and high speed recording.
Speaking of recording method which uses this ink jet recording apparatus, various types of methods have hitherto been proposed and improved: some have been placed on the market, whereas endeavors are being made to put others to practical use.
Above all, it is demanded to lower a manufacturing cost and improve discharging performance of a recording head of a type which comprises as an ink jet recording head, a substrate having an energy generating element for generating an ejecting energy and a ceiling plate joined to the substrate for forming a liquid flow path for discharging ink and a liquid chamber.
In order to meet a demand described above, the inventor et al. have manufactured a recording head shown in FIG. 10. FIG. 10 is a sectional view taken in a direction of a flow path showing a configurational example of an ink discharge unit constituting a background art of the present invention and FIG. 11 is an enlarged view of a vicinity of a liquid chamber shown in FIG. 10. Furthermore, FIGS. 12A, 12B and 12C are diagrams showing a form of the liquid chamber: FIG. 12A being a view as seen from a side of a discharge port, FIG. 12B being a top view and FIG. 12C being a side view.
As shown in FIGS. 10 and 11, the background art is configured by a base plate 1 made of a metal such as aluminum, a heater board 2 which is disposed on the base plate 1 and composed of a silicon substrate or the like on which a heater array for discharging ink is arranged, a printed wiring board 10 for transmitting an electric signal to the heater array on the heater board 2 by way of a bonding wire 11, a plurality of discharge ports 3 for discharging ink, a plurality of flow paths 4 which communicate with the plurality of discharge ports 3 respectively and supply the ink to the discharge ports 3, a liquid chamber 5 which communicates with the flow paths 4 and holds the ink to be supplied to the flow paths 4, a supply path 6 which communicates with an ink tank (not shown) and supplies ink from the ink tank to the liquid chamber 5, a supply tube 9 which forms the supply path 6, a grooved ceiling plate 7 which integrally forms the flow paths 4, the liquid chamber 5 and a portion of the supply path 6, and a clamp spring 8 which fixes the grooved ceiling plate 7: the discharge port 3 being formed by a laser boring method after the flow paths 4, the liquid chamber 5 and the portion of the supply path 6 are formed in the grooved ceiling plate 7 by plastic molding. Furthermore, the liquid chamber 5 is communicated with the supply path 6 by an opening 13 as shown in FIGS. 12A, 12B and 12C so that the ink is supplied from the ink tank into the liquid chamber 5 by way of the opening 13.
The opening 13 of the liquid chamber 5 is formed not in a top surface of the liquid chamber 5 but in a rear surface which is opposed to the flow paths 4. It is desirable to configure the heater board 2 as small as possible in order to reduce a manufacturing cost and a size of the liquid chamber 5 is limited, but since the top surface of the grooved ceiling plate 7 must have an area which is used to fix the grooved ceiling plate 7 with the clamp spring 8 and the supply tube 9 cannot be disposed on the top surface of the liquid chamber 5, the ink is supplied from behind the liquid chamber 5.
In the ink jet cartridge which uses the ink discharge unit configured as described above, a sucking operation is first performed by a sucking device (not shown) of an ink jet recording apparatus main unit by way of the discharge port 3, whereby the ink is supplied from the ink tank into the flow path 4.
Then, the heaters on the heater board 2 generate heat on the basis of the electric signal transmitted from the printed wiring board 10, whereby a bubble is produced in the flow path 4 and the ink is discharged from the discharge port 3 under a pressure produced by the bubble.
FIGS. 13A, 13B, 13C and 13D are diagrams descriptive of a series of operations from ink discharge to suction in the ink jet cartridge which uses the ink discharge unit shown in FIG. 10.
When a heater 23 on the heater board 2 generates heat on the basis of the electric signal transmitted from the printed wiring board 10, the ink is heated and boiled by the heat in the flow path 4, thereby forming a bubble 24 on the heater 23. The ink is discharged from the flow path 4 through the discharge port 3 under a pressure produced by the bubble 24 (FIG. 13A). At this time, a small number of small bubbles 26 may be produced upstream of the flow path 4.
The small bubble (bubbles) 26 produced on the upstream side of the flow path 4 are stagnant in the liquid chamber 5 even after the bubble 24 disappears on the heater 23 (FIG. 13B).
When the heater 23 on the heater board 2 generates heat once again thereafter on the basis of the electric signal transmitted from the printed wiring board 10, the ink is heated and boiled by the heat in the flow path 4 and the bubble 24 is produced on the heater 23, and the small bubble (bubbles) 26 move upstream of the liquid chamber 5 under a pressure produced by the bubble 24 and adhere to a ceiling surface of the liquid chamber 5 together with the small bubble (bubbles) 27 coming from the supply path 6, thereby forming a bubble 14 (FIG. 13C).
An ink jet recording apparatus performs a suction recovery at an improper printing time. A bubble is removed by bringing a suction pad 28 into contact with a surface of the discharge port 3 as shown in FIG. 13D and sucking the ink out of the flow path 4.
However, the inventor et al. have found that the bubble 14 adhering to the ceiling surface of the liquid chamber 5 is not sucked but remains and a small bubble 30 also remains upstream of the flow path 4 in some cases dependently on kinds of ink since the background art forms in the liquid chamber 5 an ink flow 12 which has a high flow velocity in a region indicated by an arrow and an ink flow 29 which has a low flow velocity in the vicinity of the ceiling surface of the liquid chamber 5 at the suction time.
FIGS. 14A, 14B, 14C and 14D are diagrams descriptive in detail of the bubble 14 remaining after the operations shown in FIGS. 13A, 13B, 13C and 13D: FIG. 14A being a sectional view taken in a direction of a flow path of the ink jet cartridge, FIG. 14B being a view of the liquid chamber 5 as seen from a side of the discharge port, FIG. 14C being a top view of the liquid chamber 5 and FIG. 14D being a side view of the liquid chamber 5. The opening 13 of the liquid chamber 5 is disposed in the rear surface of the liquid chamber 5 and has a trapezoid or rectangular shape as shown in FIG. 14B. The opening 13 must have a height nearly equal to that of the liquid chamber 5 in order to reserve a sufficient sectional area without narrowing an ink flow path. Accordingly, the ink flow 12 which flows from the opening 13 into the liquid chamber 5 at the suction recovery time has a portion of a maximum flow velocity in the vicinity of a center of the opening 13 as shown in FIG. 14D and other portions of flow velocities which are slowed down outward.
Even after the above described sucking operation is performed, bubbles 14-1 and 14-2 may adhere to the ceiling surface of the liquid chamber 5 and remain as shown in FIGS. 14A, 14B, 14C and 14D.
The remaining bubble 14 may gradually expand due to a temperature rise in the ink jet cartridge due to successive printing operations and incorporation with fine bubbles coming from a side of the ink tank, thereafter leaving from a wall surface of the liquid chamber 5, reaching the flow path 4 and filling the flow path 4, thereby disabling the ink jet cartridge from discharging the ink.
Furthermore, the background art may allow the liquid chamber 5 to be filled with the bubble and disable all the flow paths from discharging the ink, thereby posing a problem in image qualities.
Though means for enhancing a sucking pressure of the ink jet recording apparatus main unit can be considered as a method to remove the bubble from the liquid chamber 5, it is difficult to enhance the sucking pressure simply since a sucking pressure which is higher than required produces a turbulent flow in the ink supply path from the ink tank to the ink discharge unit at the suction recovery time, thereby producing small bubbles due to a cavitation phenomenon contrary to a purpose.
The present invention has been achieved in view of the problems of the conventional art and has an object to provide an ink jet recording head which is capable of removing a bubble stagnant in a liquid chamber without enhancing a sucking pressure and an ink jet recording apparatus which uses the ink jet recording head.
In order to accomplish the above described object, an ink jet recording head according to the present invention is an ink jet recording head comprising a discharge port for discharging ink, a liquid flow path which communicates with the discharge port and in which a heat energy generating element for generating a heat energy to be utilized for discharging ink is disposed, a common liquid chamber which is disposed for supplying ink into the above described liquid flow path as the ink is discharged and located after the above described liquid flow path, and an ink supply port for supplying ink into the above described common liquid chamber, characterized in that the above described common liquid chamber has a curved surface convex inward of the above described liquid chamber in a region adjacent to the above described ink supply port.
Furthermore, an ink jet recording head in another mode of the present invention is an ink jet recording head comprising a substrate on which a plurality of energy generating elements for generating a discharging energy are disposed, and a ceiling plate which integrally forms a concavity having grooves composing a plurality of liquid flow paths corresponding to a plurality of discharge ports for discharging ink respectively and a common liquid chamber that communicates with the above described grooves respectively for supplying the ink to the above described plurality of liquid flow paths, and an ink supply port and is joined to the above described substrate, characterized in that the concavity of the above described ceiling plate has a curved surface which is convex toward the above described substrate in a region between the above described grooves and the above described ink supply ports.
Furthermore, an ink jet recording apparatus according to the present invention is characterized in that it comprises a carriage on which the above described ink jet recording head is mounted and performs recording on a recording medium by sliding the above described carriage on the recording medium.
Since a ceiling of a liquid chamber which holds the ink discharged from the discharge port has a curved surface convex inward in the ink jet recording head according to the present invention configured as described above, the liquid chamber has a region where its sectional area is smoothly narrowed to a location at which a bubble is stagnant in a flow direction of the ink from the ink supply port toward the ink discharge port and then smoothly enlarged. Accordingly, the ink jet recording head allows the ink to flow at a flow velocity not slowed down in the vicinity of the ceiling surface when suction recovery is performed from the discharge port, thereby exhibiting enhanced performance for removing a bubble which adheres to a surface of the ceiling.
When a maximum area of a section of the common liquid chamber perpendicular to the substrate is not larger than 2.5 times of an opening of the ink supply port, a reduction of a flow velocity of the ink introduced from the supply path into the liquid chamber is minimized at the time of suction recovery operation, thereby enhancing the performance for removing the bubble.
When a region in which a sectional area is enlarged toward the liquid chamber is reserved in the flow path at a location of communicating with the liquid chamber, the ink flows smoothly upstream of the flow path, thereby preventing a bubble from remaining in the vicinity of an upstream section of the flow path.
In addition, a form of the common liquid chamber according to the present invention wherein the ink supply port is located in a region opposed to the discharge port as described above exhibits a remarkable effect to permit removing a bubble more easily.